The renin-angiotensin system (RAS) plays an important role in circulatory homeostasis at both systemic and local levels. Angiotensin converting enzyme (ACE), a 175 kD protein known to be widely distributed throughout the cardiovascular system, has been long recognized as the key enzyme in the generation of angiotensin II, a peptide that regulates fluid balance, blood pressure and local blood flow in a number of tissues (Peach, M. J. Physiological Reviews 57:313-370 (1997)). As part of an ongoing strategy to establish genes associated with cardiovascular function via high throughput cDNA sequencing, we identified a member of the RAS family of enzymes, ACE-2, from human kidney. This enzyme was also identified in a variety of tissues by others (Donoghue et al., Circulation Research 87:e1-e9 (2000), Tipinis et al., The Journal of Biological Chemistry 275:33238-33243 (2000)). The unmodified ACE-2 protein contains transmembrane and signal peptide domains, but unlike ACE, ACE-2 contains just one single extracellular Zn+2 binding metalloprotease domain (Tipinis et al., The Journal of Biological Chemistry 275:33238-33243 (2000)). ACE-2 mRNA has a more limited expression pattern than ACE (Donoghue et al., Circulation Research 87:e1-e9 (2000)) and, remarkably, no detectable expression in lungs (unpublished data).
ACE-2 and related carboxypeptidases (Snyder et al., The Journal of Biological Chemistry 260:7857-7860 (1985); Kokkonen et al., Circulation 95:1455-1463 (1997)) catalyze the removal of the C-terminal leucine from angiotensin I to form the nonapeptide angiotensin 1-9 (A1-9) or des-Leu10-angiotensin I (Donoghue et al., Circulation Research 87:e1-e9 (2000); Tipinis et al., The Journal of Biological Chemistry 260:7857-7860 (2000); Snyder et al., The Journal of Biological Chemistry 260: 7857-7860 (1985); Snyder et al., Biochemica et Biophysica Acta 871:1-5 (1986)). Circulating A1-9 has been detected in vivo at levels twice that of angiotensin II (Oparil et al., Circulation Research 29:682-690 (1971); Johnson et al., Peptides 10:489-492 (1989)). In the case of ACE-2, the above reaction is not blocked by captopril, lisinopril or enalaprilat (Donoghue et al., Circulation Research 87:e1-e9 (2000); Tipinis et al., The Journal of Biological Chemistry 275:33238-33243 (2000)). The unique expression profile of ACE-2, spectrum of its enzymatic activity and inhibitory effects of its product A1-9 on ACE have led to the speculation that ACE-2 functions to affect circulatory homeostasis by promoting vasodilation (Donoghue et al., Circulation Research 87:e1-e9 (2000); Snyder et al., The Journal of Biological Chemistry 260:7857-7860 (1985)). However, A1-9 has been shown to be a weak vasoconstrictor in isolated rat aorta and have weak pressor activity in anesthetized rats and dogs (Oparil et al., Circulation Research 29:682-690 (1971)). Therefore, we hypothesized that one of the physiologic roles of ACE-2 is to increase arterial pressure through the actions of its catabolic product, A1-9. As such, ACE-2 might be a valid target for drug development in hypertension.
Accordingly, molecules that specifically bind ACE-2 would find a variety of uses in the study of ACE-2, angiotensin 1-9, and angiotensin, as well as ACE, and its known substrates: Angiotensin II, Angiotensin 1-7, des-Asp, bradykinin, neurotensin, and Substance P. Further, molecules that specifically bind ACE-2 would also find a variety of uses in the manufacture and purification of ACE-2, ACE, angiotensin, angiotensin II, and/or Angiotensin 1-9 in commercial and medically pure quantities, and in the development new therapeutic or diagnostic reagents. ACE-2 binding polypeptides may also find medical utility in, for example, the treatment of cardiovascular disorders (e.g., hypertension, chronic heart failure, left ventricular failure, stroke, cerebral vasospasm after subarachnoid injury, atherosclerotic heart disease, and retinal hemorrhage), renal disorders (e.g., renal vein thrombosis, kidney infarction, renal artery embolism, renal artery stenosis, and edema, hydronephritis), proliferative diseases or disorders (e.g., vascular stenosis, myocardial hypertrophy, hypertrophy and/or hyperplasia of conduit and/or resistance vessels, myocyte hypertrophy, and fibroblast proliferative diseases), inflammatory diseases (e.g., SIRS (systermic Inflammatory Response Syndromes), sepsis, polytrauma, inflammatory bowl disease, acute and chronic pain, rheumatoid arthritis, and osteo arthritis), allergic disorders (e.g., asthma, adult respiratory distress syndrome, wound healing, and scar formation), as well as several other disoders and/or diseases (e.g., periodontal disease, dysmenorrhea, premature labor, brain edema following focal injury, diffuse axonal injury, and reperfusion injury).